Tumor progression is a critical step in lymphomagenesis. It is a little-understood process. In murine lymphomagenesis we have found three distinct phases of T cell neoplasms: T cell neoplasms of phase I, which we shall call T cell lymphoblastoma (TCLB), consist of cells that are normal diploid, growth factor dependent, do not clone in soft agar, and do not grow under the skin in vivo. TCLB cells are autostimulating, genetically stable tumor cells. In contrast T cell neoplasms of phase III, which we shall call T cell lymphomas (TCL), contain cells capable of autonomous growth which can be cloned quantitatively in soft agar and which are tumorigenic when inoculated under the skin of mice. Phase III TCL cells are often trisomic for chromosome 15 and highly stable genetically; they originate in the thymus. T cell neoplasms of phase II have properties intermediate between neoplasms of phase I and phase III. The essence of progression of phase I cells to phase III consists of the gradual development of growth factor independence. Phase I cells progress to phase II and possibly to phase III cells, a process accompanied by increasing autonomy of the cells. We will study the mechanism of this progression. TCLB- and TCL cells will be tested for the expression of cellular oncogenes. Poly (A+) RNA extracted from cultured neoplastic T cells of phases I, II, and III, will be hybridized following separation on agorose gels and "Northern blotting". Nick-translated probes made to 14 different cloned oncogenes, C-type viral long terminal repeats (LTR) and viral envelope sequences will be used. The level of expression as well as gene rearrangements will be sought and correlated with chromosome abnormalities that are present in the karyotypes of the neoplastic cells of phases II and III. Expression and/or rearrangement of genes associated with T cell proliferation (e.g. interleukin-2) will also be studied, as will the phenotypic differences among TCLB and TCL cells of the three phases. Activation of transforming genes in karyotypically different TCL clones will be studied by means of DNA-mediated gene transfer. NIH 3T3- and lymphoid (TCLB) cells will be transfected with DNA isolated from TCL clones. Sensitivity to digestion with restriction enzymes of transforming DNAs isolated from different TCL clones will be used to delineate the transforming genes present in different TCL clones. Polyclonal B cell lymphoblastomas (BCLB) have been induced in B6 mice by a potent C-type virus complex. The pathogenic virus will be sought and will be molecularly cloned. Viral genes active in the induction of BCLB will be studied by constructing site-specific virus recombinants.